Previous work from this laboratory has demonstrated that when compared to the young adult rat myocardium, myocardium from aged rats exhibits a diminished inotropic response to catecholamines. The (chronotropic) response to these agents has now been expanded to both dog and man. BIBLIOGRAPHIC REFERENCE: Gerstenblith, G., Lakatta, E.G., and Weisfeldt, M.L.: Age changes in myocardial function and exercise response. Prog. Cardiovasc. Dis. 19: 1-21, 1976.